The present invention relates to an electronic component for processing high frequency signals and a method for fabricating the same and, particularly, an electronic component which can be utilized in various communication devices such as portable telephones, automobile telephones and the like and a method for fabricating the same.
Conventional high frequency circuits for processing high frequency signals above 100 MHz, for example, are formed by forming a conductive layer on a substrate using a conductive paste and then patterning the conductive layer into a predetermined circuit pattern by etching, as described in, for example, Japanese Patent Application Laid Open No. 9-199365.
Japanese Patent Publication No. 35-3723 further discloses a method for forming a conductive pattern by printing a copper paste on a substrate made of resin, drying it, and plating the copper paste with copper by electroplating.
Moreover, Japanese Patent Application Laid Open No. 4-323887 discloses a method for forming a conductive pattern by forming a copper oxide film on a substrate made of ceramic, and plating the copper oxide film with copper by PVD (physical vapor deposition).
The conductive patterns obtained by the above-mentioned prior art methods have an almost trapezoidal or rectangular cross section. High frequency characteristics (Q value) of the conductive pattern having such a cross section depends on the sectional area. To increase the cross-sectional area of the conductive pattern, it is necessary to increase the thickness or width thereof In this kind of electronic component used with high frequency signals, the conductive pattern lines have to be formed with high accuracy and narrow width. Therefore, in order to increase the cross-sectional area of the conductive pattern, it is preferable to increase the thickness thereof while keeping its width narrow. However, when the thickness of the film is increased, the following various problems arise.
When an electronic component for high frequency signals is fabricated, a number of elements for the electronic component are simultaneously formed on a single wafer. In the wafer process, however, when the thickness of the conductive paste formed on the wafer is increased, the fluctuation in the thickness thereof also increases. When the thickness of the conductive layer is set more than 10 xcexcm, 5 xcexcm fluctuation in the thickness of the conductive layer may occur in the plane of the wafer, although the fluctuation in thickness depends on various condition of forming the conductive layer. When such a fluctuation in the thickness of the conductive paste occurs, the width of the conductive pattern made of the conductive paste becomes too narrow at the portion where the thickness of the conductive layer is relatively thin, because the conductive paste is excessively etched. On the other hand short circuiting may occur due to the remaining conductive film at portions where the thickness of the conductive layer is relatively thick, because the conductive film is etched insufficiently. Product yield decreases as a result.
Further, since the conductive layer is subjected to isotropic etching, side-etching (under-etching) of the conductive layer under a resist film formed on the conductive layer is easily occurred at portions where the thickness thereof is relatively thick, thereby making it difficult to obtain conductive pattern lines of the desired width.
The probability of the wafer warping after the conductive paste is sintered because the physical stress at the interface between the conductive layer and the wafer increases as the conductive layer becomes thicker. Such warp degrades the precision of the conductive pattern made from the conductive paste because the warp weakens the contact between a mask and the main surface of the wafer.
To solve these problems, it is required to reduce the thickness of the conductive layer to less than a certain degree. This limits the high-frequency characteristics. Particularly, it is difficult to restrain signal loss caused by the skin effect occurring in the high frequency range.
Furthermore, because of the cross section of the conductive pattern is almost rectangle or trapezoid, localization of electric current cannot be avoided. Such localization of electric current causes a localization of the high frequency magnetic field, so that a conductor loss can not be improved.
It is therefore an object of the present invention to provide an improved electronic component for high frequency signals and a method for fabricating the same.
Another object of the present invention is to provide an electronic component for a high frequency signal with good high frequency characteristics and a method for fabricating the same.
Another object of the present invention is to provide an electronic component for a high frequency signals and a method for fabricating the same in which a signal loss caused by the skin effect can be lowered.
Another object of the present invention is to provide an electronic component for high frequency signals and a method for fabricating the same in which local concentration of the high frequency magnetic field can be reduced so that characteristic degradation due to local concentration of the high frequency magnetic field can be prevented.
Another object of the present invention is to provide a method for fabricating an electronic component for high frequency signals that enables improved production yield.
Another object of the present invention is to provide a method for fabricating an electronic component for high frequency signals that enables improved production yield by preventing over-etching and short-etching.
Another object of the present invention is to provide a method for fabricating an electronic component for high frequency signals that improves contact between a mask and a main surface of a wafer and thus improves accuracy of the conductive pattern.
The above and other objects of the present invention can be accomplished by an electronic component for high frequency signals comprising an insulating substrate and a conductive pattern formed on the insulating substrate, the conductive pattern having a dual structure including a first element and a second element, the second element of the conductive pattern covering the first element of the conductive pattern substantially entirely.
According to the present invention, the cross-sectional area of the conductive pattern can be increased easily because the conductive pattern has a dual structure. Therefore, an electronic component having good high frequency characteristics can be obtained.
In a preferred aspect of the present invention, the first element of the conductive pattern has a side wall and the second element of the conductive pattern has a dilated portion expanded outward from the side wall of the first element.
According to this preferred aspect of the present invention, because second element of the conductive pattern has the dilated portion, signal loss caused by the skin effect can be reduced, thereby improving the high frequency characteristic.
In a further preferred aspect of the present invention, the dilated portion is approximately arc-shaped.
According to this preferred aspect of the present invention, signal loss caused by the skin effect can be more effectively reduced.
In a further preferred aspect of the present invention, the first element of the conductive pattern has a contact portion contacting with the insulating substrate, an edge of the contact portion of the first element and an edge of the dilated portion of the second element being substantially coincident.
According to this preferred aspect of the present invention, even if over-etching or side-etching of first element occurs, the over-etched portion or the side-etched portion of first element can be effectively repaired. Moreover, signal loss caused by the skin effect can be more effectively reduced. Furthermore, local concentration of the high frequency magnetic field can be more effectively avoided.
In a further preferred aspect of the present invention, the first element and the second element include the same constitutions.
According to this preferred aspect of the present invention, adhesion between the first element and the second element can be strengthened.
In a further preferred aspect of the present invention, the first element includes at least one component selected from the group consisting of Cu, Ag, and Au.
In a further preferred aspect of the present invention, the first element includes Cu as a main constituent.
According to this preferred aspect of the present invention, aqueous solution of ferric chloride (FeCl3), a commonly utilized etchant, can be used to etch the first element.
In a further preferred aspect of the present invention, the first element also includes Pd.
In a further preferred aspect of the present invention, the first element is formed by photolithography.
In a further preferred aspect of the present invention, the second element is formed by electroless plating.
In a further preferred aspect of the present invention, the conductive pattern has a coil pattern which works as an inductor.
In a further preferred aspect of the present invention, the electronic component comprises an insulating layer covering. at least a part of the conductive pattern and an upper pattern formed on the insulating layer.
In a further preferred aspect of the present invention, the upper pattern is electrically connected to the conductive pattern through a via hole formed in the insulating layer.
In a further preferred aspect of the present invention, a part of the conductive pattern, a part of the upper pattern, and a part of the insulating layer sandwiched between the part of the conductive pattern and the part of the upper pattern work as capacitor.
In a further preferred aspect of the present invention, the electronic component further comprises a dielectric layer entirely formed on the insulating substrate such that the dielectric layer is interposed between the insulating substrate and the conductive pattern.
According to this preferred aspect of the present invention, a smooth and flat surface on which the conductive pattern is formed can be obtained so that the pattern accuracy of the conductive pattern can be improved.
In a further preferred aspect of the present invention, the dielectric layer is made of a sintered dielectric paste including a glass constituent and a ceramic constituent.
In a further preferred aspect of the present invention, the sintering temperature of the dielectric layer is not greater than that of the insulating substrate.
According to this preferred aspect of the present invention, because the sintering temperature of the dielectric layer is not greater than that of the insulating substrate, the insulating substrate is not damaged by heat during the sintering of the dielectric layer.
In a further preferred aspect of the present invention, the sintering temperarture of the conductive pattern is not greater Than that of the dielectric layer.
According to this preferred aspect of the present invention, because the sintering temperature of the conductive pattern is not greater than that of the dielectric layer, the dielectric layer is not damaged by heat during the sintering process of the conductive pattern.
The above and other objects of the present invention can be also accomplished by an electronic component for high frequency signals comprising an insulating substrate, a dielectric layer formed over the entire surface of the insulating substrate and a conductive pattern formed on the dielectric layer, the dielectric layer being made from a sintered dielectric paste including a glass component and a ceramic constituent.
According to the present invention, a smooth and flat surface on which the conductive pattern is formed can be easily obtained so that the pattern accuracy of the conductive pattern can be improved.
In a preferred aspect of the present invention, the dielectric layer includes a pigment.
According to this preferred aspect of the present invention, because the dielectric layer includes the pigment, reflection of light used in photolithographic processing can be effectively avoided, thereby improving the patterning accuracy.
In a further preferred aspect of the present invention, the amount of the pigment contained into the dielectric layer is about 5 wt %.
In a further preferred aspect of the present invention, the content ratio of the ceramic constituent to the glass constituent is 25 vol % to 35 vol %.
In a further preferred aspect of the present invention, the conductive pattern includes at least one constituent selected from the group consisting of Cu, Ag, and Au.
In a further preferred aspect of the present invention, the conductive pattern includes Cu as a main constituent.
According to this preferred aspect of the present invention, an aqueous solution of ferric chloride (FeCl3), a commonly utilized etchant, can be used to etch the conductive pattern.
In a further preferred aspect of the present invention, the conductive pattern having a dual structure including a first element and a second element, the second element of the conductive pattern covering the first element of the conductive pattern substantially entirely.
According to this preferred aspect of the present invention, the cross-sectional area of the conductive pattern can be increased easily because it has the dual structure. Therefore, an electronic component having good high frequency characteristics can be obtained.
In a further preferred aspect of the present invention, the first element and the second element include the same constituents.
According to this preferred aspect of the present invention, adhesion between the first element and the second element can be strengthened.
In a further preferred aspect of the present invention, the sintering temperature of the dielectric layer is not greater than that of the insulating substrate.
According to this preferred aspect of the present invention, because the sintering temperature of the dielectric layer is not greater than that of the insulating substrate, the insulating substrate is not damaged by heat during the sintering process of the dielectric layer.
In a further preferred aspect of the present invention, the sintering temperature of the conductive pattern is not greater than that of the dielectric layer.
According to this preferred aspect of the present invention, because the sintering temperature of the conductive pattern is not greater than that of the dielectric layer, the dielectric layer is not damaged by heat during the sintering process of the conductive pattern.
The above and other objects of the present invention can be also accomplished by a method for fabricating an electronic component for high frequency signal, comprising:
a providing step for providing an insulating substrate;
a forming step for forming a conductive paste on the insulating substrate;
a patterning step for patterning the conductive paste formed on the insulating substrate to form a first conductive pattern; and
a plating step for forming a second conductive pattern covering the first conductive pattern.
According to the present invention, the sectional area of the conductive pattern composed of the first conductive pattern and the second conductive pattern can be easily increased because the second conductive pattern is formed on the first conductive pattern by the plating step. The electronic component fabricated according to the present invention therefore has good high frequency characteristics.
In a preferred aspect of the present invention, the patterning step is performed by photolithography.
According to this preferred aspect of the present invention, because the plating step is performed to form second conductive layer on the first conductive layer after the patterning step has been completed, the patterning step can be performed without difficulty.
In a further preferred aspect of the present invention, the plating step is performed by electroless plating method.
According to this preferred aspect of the present invention, because the cross-sectional shape of the second conductive pattern can be approximately arc-shaped, signal loss caused by the skin effect can be reduced, thereby improving the high frequency characteristics.
In further preferred aspect of the present invention, the method for fabricating an electronic component further comprises a heating step for heating the second conductive pattern.
According to this preferred aspect of the present invention, the resistivity of the second conductive pattern can be lowered.
In a further preferred aspect of the present invention, the heating step is performed at 300 to 900xc2x0 C.
The above and other objects of the present invention can be also accomplished by a method for fabricating an electronic component for high frequency signals, comprising:
a first sintering step for sintering an inorganic material to form an insulating substrate;
a coating step for coating a dielectric paste on the insulating substrate;
a second sintering step for sintering the dielectric paste to form a dielectric layer; and
a forming step for forming a conductive pattern on the dielectric layer.
According to the present invention, a smooth and flat surface on which the conductive pattern is formed can be easily obtained, thereby improving the pattern accuracy of the conductive pattern.
In a preferred aspect of the present invention, the first sintering step and the second sintering step are performed at a first and a second temperature, respectively, the second temperature being not greater than the first temperature.
According to this preferred aspect of the present invention, because the second temperature is not greater than first temperature, the insulating substrate can be prevented from damage by the second sintering step.
In a further preferred aspect of the present invention, the forming step includes a third sintering step for sintering a conductive paste, the third sintering step being performed at a third temperature which is not greater than the second temperature.
According to this preferred aspect of the present invention, because the third temperature is not greater than second temperature, the dielectric layer can be prevented from damage by the third sintering step.
The above and other objects and features of the present invention will become apparent from the following description made with reference to the accompanying drawings.